sorry im a newbe but im also irish so im woundering what you refer to as a crumb coat?? i dont no if its that i just havnt heard of it before or its an american version of somthing we call something else. ..
do ye crumb coat a cake then butter cream it(i no what butter cream is) then cover in fondant..?

but what does a crumb coat consist of?

it's a thin coat of icing put on first and allowed to crust so that seals in the crumbs and prevents then from getting into the final coat of icing.

so its a thin coat of buttercream left to crust then more buttercream addedbrfore fondant.. have i it right?

yep. exactly